Application of generalized singular value decomposition to ionospheric tomography

The electron density distribution of the low- and mid-latitude ionosphere has been investigated by the com- puterized tomography technique using a Generalized Singu- lar Value Decomposition (GSVD) based algorithm. Model ionospheric total electron content (TEC) data obtained from the International Reference Ionosphere 2001 and slant rela- tive TEC data measured at a chain of three stations receiv- ing transit satellite transmissions in Alaska, USA are used in this analysis. The issue of optimum efficiency of the GSVD algorithm in the reconstruction of ionospheric structures is being addressed through simulation of the equatorial ioniza- tion anomaly (EIA), in addition to its application to investi- gate complicated ionospheric density irregularities. Results show that the Generalized Cross Validation approach to find the regularization parameter and the corresponding solution gives a very good reconstructed image of the low-latitude ionosphere and the EIA within it. Provided that some mini- mum norm is fulfilled, the GSVD solution is found to be least affected by considerations, such as pixel size and number of ray paths. The method has also been used to investigate the behaviour of the mid-latitude ionosphere under magnetically quiet and disturbed conditions. A radio signal passing through the ionosphere suffers time delay, refraction and polarization rotations during its pas- sage through the ionized plasma. Since the beginning of the satellite era, radio beacons on board artificial satellites have been routinely used to measure the total ionospheric elec- tron content (TEC) using techniques such as Faraday rota- tion, group delay, Doppler shift (de Mendonca and Garriott, 1962; Davies, 1980, 1989, etc.). TEC is a measure of the total number of electrons contained in a tube of unit cross sectional area along the line of sight from the transmitter to the receiver. Individual and coordinated TEC measurements provide information about the temporal and horizontal distri- bution of electron content on various time scales. However,